1. Field of the Invention
The present invention relates to an apparatus for determining a collision for an air bag of a car, and particularly, to one capable of preventing an erroneous deployment of the air bag when the car is driving along a rough road.
2. Description of the Related Art
An apparatus for determining a collision for an air bag of a car has an acceleration sensor to detect deceleration at a collision. The apparatus processes a signal from the acceleration sensor, and if the air bag must be deployed, provides an ignition signal at proper timing. The acceleration sensor detects collision energy as deceleration. The apparatus integrates the deceleration signal while the signal is being above a threshold, and when the integral reaches a given value, generates an ignition signal. When the car is driving at a speed of below 13 km/h, collision energy is too small to deploy the air bag. Accordingly, collision deceleration at such a low speed is used as a threshold to determine whether or not the air bag must be deployed. A low-speed collision that requires no deployment of the air bag is an OFF collision, and a collision that needs the air bag is an ON collision.
When the car is driving along a rough road, the acceleration sensor may provide a deceleration signal. The signal sometimes exceeds the threshold, to indicate the ON collision. To prevent an erroneous deployment of the air bag on the rough road, the threshold must be high. This, however, delays a deployment of the air bag at the ON collision on a normal road.